【BZOJ 4580】【Usaco2016 Open】248

http://www.lydsy.com/JudgeOnline/problem.php?id=4580
区间dp，f(i,j)表示区间[i,j]全部合成一个数，这个数是多少。
可以归纳证明[i,j]如果可以合成一个数，那么只能合成这一个数

#include<cstdio>
#include<cstring>
#include<algorithm>
using namespace std;

const int N = 253;

int n, a[N], f[N][N];

int main() {
	scanf("%d", &n);
	for (int i = 1; i <= n; ++i)
		scanf("%d", a + i);
	for (int i = 1; i <= n; ++i)
		f[i][i] = a[i];
	
	for (int i = n - 1; i >= 1; --i)
		for (int j = i + 1; j <= n; ++j)
			for (int k = i; k < j; ++k)
				if (f[i][k] && f[k + 1][j] && f[i][k] == f[k + 1][j]) {
					f[i][j] = f[i][k] + 1;
					break;
				}
	
	int ans = 0;
	for (int i = n; i >= 1; --i)
		for (int j = i; j <= n; ++j)
			ans = max(ans, f[i][j]);
	
	printf("%d\n", ans);
	return 0;
}